This application claims the priority of German Patent Application, Ser. No. 101 34 972.6-14, filed Jul. 24, 2001, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a flow regulating apparatus for a fluid, in particular a pneumatic choke valve.
German patent publication DE 199 32 982 A1 describes a pneumatic choke valve having a choke duct in the form of an inner cylinder for fluidly connecting an inlet port and an outlet port. Disposed in the choke duct is a cylindrical throttling piston which can be moved in longitudinal direction from outside. Normally, the throttling piston can be moved between two end positions. The throttling piston is configured to define an annular gap as overflow passage in the area of the choke duct edge. The cross section of the annular gap is hereby dependent on the axial position of the throttling piston.
German Pat. No. DE 33 42 405 C2 describes a choke valve having a throttling piston and a confronting contact surface of conical configuration to realize a degressive increase of the cross section of the overflow passage during movement of the throttling piston from an initial position to the end position. The cross sectional area as a function of the piston stroke produces in this type of choke valve a degressive characteristic line. In this way only a soft movement is effected at the moment of opening and closing because the conical configuration of the throttling piston and the confronting contact surface prevents the normally encountered suction and a resultant added acceleration of the piston.
When a hoist, in particular a pneumatically operated balancing hoist, is involved, the use of such a throttling piston does not enable a precise control for elevating and lowering small loads.
It would therefore be desirable and advantageous to provide an improved flow regulating apparatus for application with a pneumatically operated balancing hoist, to obviate prior art shortcomings and to allow a precise control for elevating and lowering small loads.
According to one aspect of the present invention, a flow regulating apparatus for a fluid, in particular a pneumatic choke valve, includes a housing having an inlet port and an outlet port fluidly connected by a choke channel, and a throttling piston disposed in the choke channel for movement in longitudinal direction between an initial position and an end position, wherein the throttling piston includes a tapered section to define with the choke channel an overflow passage whose cross section is dependent on a position of the throttling piston, wherein the tapered section is configured such that a movement of the throttling piston from the initial position to the end position results in a progressive increase of the cross section of the overflow passage.
The present invention resolves prior art problems by so providing the throttling piston with a taper as to realize a progressive increase of the cross section of the overflow passage during movement of the throttling piston from the initial position to the end position. The progressive increase of the overflow cross-section causes the volume flow, during even displacement of the throttling piston, to rise relatively slowly at the beginning and then to rise increasingly faster. As a result, when incorporated in a balancing hoist, a very sensitive and precise control for elevating and lowering a load is realized.
According to another feature of the present invention, the throttling piston has one end which may project out of the housing to form an actuating member actuatable by an operator for longitudinal movement of the throttling piston by means of an operator""s thumb.
According to another feature of the present invention, the throttling piston may have a cylindrical configuration formed with the tapered section which extends radially and progressively decreases in a longitudinal direction, wherein the choke channel forms a cylindrical hollow space corresponding to the throttling piston. In this way, the overall fabrication is simplified.
According to another feature of the present invention, the throttling piston may be constructed to have three length portions, namely a cylindrical leading portion having an outer diameter, which is smaller than an inner diameter of the choke channel to thereby bound an annular gap to form the overflow passage in the area of the initial position, a central portion which includes an initial zone of the tapered area and defines the progressively increasing cross section of the overflow passage, and an end portion having a conical configuration defined by a steep cone angle for utilization a greatest possible pressure drop between the inlet port and the outlet port.